The Consumer Financial Protection Bureau issued a final rule Wednesday that allows it to monitor the biggest nonbank auto finance companies.

The rule, which largely mirrored an earlier proposal, extends CFPB supervision to any nonbank auto finance company involved in either making, acquiring or refinancing 10,000 or more leases per year.

"Auto loans and leases are among the most significant and complex financial transactions in a typical consumer's life," said CFPB Director Richard Cordray in a news release Wednesday. "Today's rule will help ensure that larger auto finance companies treat consumers fairly."

With about $900 billion in auto loans outstanding as of the fourth quarter of 2014, such loans are the third largest category of household debt. The market also continues to grow as more than a fourth of new cars purchased are done so with leases.

Previously, the CFPB only oversaw auto financing through the largest banks and credit unions. The rule will give the regulator oversight of 34 nonbank auto finance companies and their affiliates, which originate roughly 90% of nonbank auto loans and leases, the CFPB estimated.

In tandem with the rule, the CFPB also released new exam procedures that will gauge auto finance companies' compliance and a manual that lays out how the monitoring process will work.

The agency will check to see whether auto finance companies market their products fairly and disclose auto financing terms. They will also make sure that these businesses provide correct information to credit bureaus, appropriately collect debts and lend fairly.

The rule will go into effect two months after it is published in the Federal Register.